1. Field of the Invention
The present invention relates, in general, to electric power service to homes and buildings and, more specifically, to overvoltage and/or overcurrent devices used with watthour meters mounted in watthour meter sockets at homes and buildings.
2. Description of the Art
Electrical power is supplied to an individual site or service by external electrical power line conductors located above or below ground. In a conventional arrangement, electrical power line conductors are connected to contacts in a watthour meter socket mounted on a building wall. Electrical load conductors are connected to another set of contacts in the meter socket and extend to the electrical distribution network in the building. A watthour meter is connected into the contacts in the meter socket to measure the electric power drawn through the load conductors.
Due to the current trend toward the use of plug-in watthour meters, A to S type socket adapters have been devised which convert A-base type bottom connected watthour meter sockets to receive plug-in watthour meters. Another type of socket adapter has been devised which allows the installation of other devices between the watthour meter socket and a plug-in watthour meter.
Such watthour meter socket adapters have also been provided with power disconnect devices, such as circuit breakers or ground fault circuit interrupters, both for protecting the electrical service as well as, in certain applications, to limit the amount of power supplied to the site. Such power disconnect devices may include an elongated plunger, the end of which extends outwardly through an opening in the annular side wall of the socket adapter when the circuit breaker is in the open or power disconnected position. The exposed end of the plunger can be pushed through the side wall of the watthour meter socket adapter to close the circuit breaker and to reapply power to the site. In certain of these devices, the ends of the plungers extending through the sidewall of the adapter have been colored red for high visibility of a tripped or open condition of the circuit breaker, etc.
Many older homes and buildings, even where originally wired with bottom connected watthour meters, have been converted by electrical utilities to socket style meters by the use of the above-described A to S socket adapter. This type of socket adapter does not require the existing wires to be moved which could cause the insulation which has become brittle with age to fall apart exposing the conductor. If this happens, the conductors and the socket itself need to be replaced which is a time consuming and costly process. This also creates further problems since the service entrance cables into the building should also be replaced and so on down the line through the distribution network as individual conductors are moved.
Currently, homes and buildings often have various electrically powered devices, such as a large number of appliances, computers, medical systems, video display systems, etc., which were not envisioned when the original distribution network conductors were sized to meet a particular maximum load at the time of the original installation. Older homes and buildings have been wired with smaller gauge wires, as small as #12 AWG, with up to and including #6 AWG also being common. The amperage usage in many of these systems exceeds the safe capacity of the individual wires or conductors. Further, due to the age of such wiring installations, the insulation on the individual wires typically is brittle and any movement of the wires for service upgrade could lead to the aforementioned deterioration or separation of the insulation from the wires which could lead to arcing between adjacent conductive elements and electrical fires.
One method to reduce fires in older installations where the insulation on the system wires is deteriorating is to prevent the system voltage levels from becoming too high and arcing. A socket type watthour meter has built-in surge air gaps will generally arc across the gaps at about 2,500 to 5,000 volts in the event of a voltage surge or transient thereby protecting the wiring system up to this voltage level. However, surge or transient voltages less than this level can often cause arcing between the building wires where the wire insulation has deteriorated. Once arcing begins, the arc itself can eventually form a conductive path and fault thereby creating a potential fire hazard. Of course, it is also important that voltage surges and transients be blocked from the distribution system to protect the electrical appliances and electronic devices attached thereto.
To address this problem, current limiting fuses and circuit breakers have been connected by small wires between the load jaw contacts and load blade terminals in the socket adapter to create an open circuit at excessive amperage levels. Other surge voltage limiting devices have been connected between the line jaw contacts or blade terminals and ground to shunt voltage surges and transients to ground before such excessive voltages reach the watthour meter or load distribution network.
One such watthour meter base surge suppression system is disclosed in U.S. Pat. No. 5,023,747, assigned to EFI Electronics Corporation, Salt Lake City, Ut. In this device, a pair of surge suppressors in the form of metal oxide varistors are each connected to an electrical contact element which contains a slot to enable the contact element to be disposed about and in contact with the line blade terminals extending from the jaw contacts in the shell of the socket adapter through the base and outward for insertion into the jaw contacts of a watthour meter socket. Voltage surges present on the line blade terminals are conducted via the metal oxide varistors to respective fuses in the form of fusible links and then to ground to prevent the surges from being transmitted through the watthour meter and onto the electrical load distribution network. This surge suppression system also includes a diagnostic circuit which couples the varistors to an audible signal generator, such as a buzzer, which indicates that one of the fusible links has ruptured upon the occurrence of a line surge.
While this watthour meter surge suppression system has proven to be effective, it is believed that further improvements could be made to such a system to enhance the overvoltage and overcurrent protection of an electrical power service.
Thus, it would be desirable to provide a watthour meter socket adapter having both overvoltage and overcurrent protection which can be installed in a watthour meter socket without disturbing existing socket wiring. It would also be desirable to provide a watthour meter socket adapter which provides both overvoltage protection on the load side of a watthour meter and overcurrent protection on the line side of the watthour meter. It would also be desirable to provide such a watthour meter socket adapter which has lockout features with a visual lockout indicator to insure that electrical power is completely disconnected from the load distribution network during wiring changes,